Extreme mass ratio inspiral

Extreme mass ratio inspiral (or EMRI) events are the GW-driven inspiral of a "small" (1 - 100 solar mass) compact body into a massive (roughly 105 to 107 solar mass) black hole. The small body spends on the order of a year or so spiraling through the deep strong field of the large black hole; the waves that they generate in this year are particularly ornate, carrying (in principle) a detailed map of the characteristics of the strong-field spacetime of the large black hole. (Note that regular non-compact stars in this mass range don't work as well since they exhibit very strong tidal interactions with the big black hole, including full tidal disruption. Regular stars falling into black holes are really interesting and important for certain problems in astronomy, but aren't what we focus on here.)

Members of the Hughes group have spent many hours working on techniques for modeling EMRI systems, including the development of some nice audio representations of their waves. Our results are organized by the character of the orbit, and by the spin of the larger black hole. According to general relativity, a black hole of mass M can have a spin angular momentum no larger than GM2/c; for each orbit class, we have results for a few particular values of the black hole spin.

Circular inspiral

These sounds correspond to an EMRI which initially has zero eccentricity. If an orbit starts out circular, it stays circular, which makes computing its GWs relatively simple. This is a somewhat idealized limit, but nicely illustrates the dynamics of these binaries, and the character of their waves. (And, there are some astrophysical scenarios which make very small eccentricity plausible. Because such waves are relatively simple to model, they may be easier to measure, even if rare, as compared to the generic case.)

Spin 99.8% of maximum

Spin 35.94% of maximum

Generic inspiral

It is generally thought that EMRI events will have significant eccentricity and inclination. Modeling these waves is in relative infancy right now. The best sound files that we have available are produced from so-called "kludge" waves, in which a fairly crude approximation to the wave emission is used to evolve a binary's characteristics. (And, to be perfectly forthright, the kludge has itself been improved over time; the wave models we have at present are particularly kludgy kludges.) This will be updated as our work progresses!

Kludged generic inspiral